Add support flattening package hierarchy.

Based on http://go/r8-pkg-obfuscation, this CL implements flattening
(as well as repackaging) packages (in a slightly different way).

* Repackaging
In ClassNameMinifier constructor, a top-level state is introduced.
That top-level state's target package prefix is user-given.
Then, when searching for a state for any can-be-renamed classes,
that top-level state is returned, hence all those classes share the same
name space.

* Flattening
The only difference is, for different packages, different states are
created and mapped whose package prefix is suggested by the top-level
state.  That is, classes in each pacakge are still in different name
spaces, while those packages share the same top-level name space.

Bug: 37764746
Change-Id: I37246fecbbbaa38a85cd6701d368072beead478b
11 files changed
tree: 7ccf4642797c7cee30511b2bc5fcd2bce73c1c15
  1. .gitignore
  6. build.gradle
  7. buildSrc/
  8. codereview.settings
  9. copyAdditionalJctfCommonFiles.gradle
  10. scripts/
  11. src/
  12. tests/
  13. third_party/
  14. tools/

D8 dexer and R8 shrinker

The R8 repo contains two tools:

  • D8 is a dexer that converts java byte code to dex code.
  • R8 is a java program shrinking and minification tool that converts java byte code to optimized dex code.

D8 is a replacement for the DX dexer and R8 is a replacement for the Proguard shrinking and minification tool.

Downloading and building

The R8 project uses depot_tools from the chromium project to manage dependencies. Install depot_tools and add it to your path before proceeding.

The R8 project uses Java 8 language features and requires a Java 8 compiler and runtime system.

Typical steps to download and build:

$ git clone
$ cd r8
$ tools/ d8 r8

The tools/ script will bootstrap using depot_tools to download a version of gradle to use for building on the first run. This will produce two jar files: build/libs/d8.jar and build/libs/r8.jar.

Running D8

The D8 dexer has a simple command-line interface with only a few options.

The most important option is whether to build in debug or release mode. Debug is the default mode and includes debugging information in the resulting dex files. Debugging information contains information about local variables used when debugging dex code. This information is not useful when shipping final Android apps to users and therefore, final builds should use the --release flag to remove this debugging information to produce smaller dex files.

Typical invocations of D8 to produce dex file(s) in the out directoy:

Debug mode build:

$ java -jar build/libs/d8.jar --output out input.jar

Release mode build:

$ java -jar build/libs/d8.jar --release --output out input.jar

The full set of D8 options can be obtained by running the command line tool with the --help option.

Running R8

R8 is a Proguard replacement for whole-program optimization, shrinking and minification. R8 uses the Proguard keep rule format for specifying the entry points for an application.

Typical invocations of R8 to produce optimized dex file(s) in the out directory:

$ java -jar build/libs/r8.jar --release --output out --pg-conf proguard.cfg input.jar

The full set of R8 options can be obtained by running the command line tool with the --help option.


Typical steps to run tests:

$ tools/ --no_internal

The tools/ script will use depot_tools to download a lot of tests and test dependencies on the first run. This includes prebuilt version of the art runtime on which to validate the produced dex code.

Getting help

For questions, bug reports and other issues reach out to us at